The present invention relates to a method and device for separating two liquid phases that constitute a liquid mixture, which may be contaminated with solids, by means of a centrifuge with a bowl equipped with a stack of disks, with the inside diameter of the stack of disks communicating with an outlet for the light phase and with a diversion channel leading from the periphery of the stack of disks into a central chamber that communicates with an outlet for the heavy phase, whereby the radial position of the zone of separation that evolves between the two liquid phases inside the bowl can be varied by supplying additional heavy phase.
A method and device of this kind are known from German Pat. No. 874 427. The additional supply of heavy phase is controlled as a function of the radial position of the free level of liquid in the central chamber, which communicates with the heavy-phase outlet. This method of control is possible only in relation to product mixtures with phases that differ sufficiently in density and with properties that alter only insignificantly. Otherwise, the zone of separation will migrate impermissibly even though the position of the free level of liquid in the central chamber remains constant, and heavy phase can get into the light-phase outlet or vice versa.
When heavy oils are clarified in a centrifuge for example, the density of the oil and that of the water it contains are so similar that even extremely small variations in the density, temperature, or viscosity of the oil can lead to such impermissible migrations of the zone of separation. The known device is accordingly inappropriate for maintaining the zone of separation in a constant position.